The proposed research is aimed at characterizing a specialized subset of neurons in the olfactory epithelium. These D neurons appear to be unique in expressing a novel signal transduction pathway (guanylyl cyclase, GC- D) among olfactory receptor cells. These neurons may also be involved in mediating suckling behavior in neonatal rodents. The applicant proposes to: 1) isolate D neurons and characterize the signal transduction pathway and receptor molecules expressed in these cells; 2) show that GC-D is necessary for the normal expression of tyrosine hydroxylase (TH) in the olfactory bulbs, as an indicator of afferent activity; 3) examine the projection patterns of D neurons; and 4) show that GC-D neurons are necessary for nipple attachment and suckling in neonatal mice. These aims are related in an attempt to associate a specific subset of olfactory receptor cells, with unique signal transduction, to a particular set of neonatal behaviors. GC-D knockout/knockin mice will be generated to carry out the proposed experiments to identify D neurons, which make up less than 1% of olfactory receptor cells. A variety of molecular biological techniques will be used to screen isolated D neurons for the receptors and signal transduction components and use histochemical techniques for identifying projection patterns of D neurons and TH in the olfactory bulbs. In addition, GC-D transgenic mice will be used to examine the ability of neonates to attach to nipples and suckle.